Method for preparing pressure-sensitive filler-containing copying paper and paper thereof



United States Patent 0 3,330,722 METHOD FOR PREPARING PRESSURE-SENSITIVE FILLER-CONTAINING COPYING PAPER AND PAPER THEREOF Masahiro Amano and Hideo Ohye, Kobe, Japan, assignors to Mitsubishi Paper Mill, Ltd., Tokyo, Japan, a corporation of Japan No Drawing. Filed Aug. 26, 1964, Ser. No. 392,329 Claims priority, appiication Ja an, Get. 31, 1963, 38/ 57,653 12 Claims. (Cl. 162-181) This invention relates to a method for preparing an internally filled paper adapted for forming a pressuresensitive copying paper by filling a paper stock with clays of electron acceptor, which develop color by adsorbing colorless compounds of electron donor together with at least one cobalt-, manganese-, or lead-compound and to a paper thus prepared. More particularly this invention relates to a novel method for preparing an internally filled paper for forming a pressure-sensitive, copying paper in which compounds of cobalt, manganese, and lead which have been used extensively as a dryer of printing ink for a long time, are incorporated as sensitizers for color developing reaction with clays of electron acceptor, and to a paper thus prepared.

The conventional pressure-sensitive copying paper which utilizes color development by electron donating and accepting consists of a sheet of paper, the back surface of which constitutes an electron donating surface and another sheet of paper, the surface of which constitutes an electron accepting surface. The electron donating surface is coated with a particulated and individually insulated solution of colorless electron donor compounds such as a triphenyl methane phthalide compound, e. g. crystal violet lactone, and an acyl leuco methylene blue compound, e.g. benzoyl leuco methylene blue or the like dissolved in nonpolar solvents such as chlorinated diphenyl or the like, the insulation of particulated solution being performed by the coating thereof with film forming materials such as gelatine, agar-agar, albumin, salt of alginic acid, fibrinogen, casein, soya-bean protein, pectin, gum arabic, starch, starch acetate-phthalate, cellulose acetate phthalate, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polystyrene, polyacrylic ester, polymethacrylic ester, polyvinyl acetate, polyethylene imine, divinyl benzene polymer, polyethylene-m-aleic anhydride copolymer, polymethylether-maleic anhydride copolymer, etc. and the electron accepting surface is coated with electron accepting clays such as attapulgite, terra alba, activated clay, finely divided silicic acid, kaoline, pyrophillite, halloysite, zeolite, bentonite etc.

Color is developed when the insulating coating of the electron donating surface, -i.e., the capsule is broken at the contact of the two surfaces due to the local pressure exerted by writing, printing, etc., and the exuded solution is adsorbed by the electron accepting surface. Such electron accepting surfaces of pressure-sensitive copying paper have been made by coating papers with electron accepting clays such as attapulgite, terra alba, acid-treated product thereof (material produced by grinding crude or dried terra alba or similar clay, treating it by hydrochloric ac-id, nitric acid, sulfuric acid or the like at a temperature higher than 90 C., at atmospheric pressure or above and if necessary neutralizing with alkali, and after filtration and washing, drying at a temperature of from 120 C. to 200 C. and grinding) together with adhesives such as starch, casein, latex or the like. The manufacture of these accepting surfaces, however, requires two steps, i.e., paper making and coating and due to various accidents which may occur frequently during the coating step, the reduction of production efficiency has been inevitable. Assuming that electron accepting clays be filled in paper, it seems to have the possibility of improving the production efficiency, but in reality electron accepting clays filled in paper are exceedingly inferior to that coated on paper.

An object of the present invention is to provide a method for preparing a filler-containing copying paper having the same color developing function as the conventional coated paper by a filling process, in other Words, by the paper making step of the process alone, thereby to increase the production efiiciency.

Another object of the present invention is to provide such a filler-containing paper adapted for use as a pressure-sensitive copying paper.

These and other objects will be attained by the present method.

According to the present invention, a filler-containing copying paper is made by filling clays of electron acceptor into paper together with compounds of cob-alt, manganese, and lead or a mixture thereof which have been used extensively as dryers of printing ink for a long time.

Compounds of cobalt, manganese, and lead used in the present invention strengthen the color developing reaction not only by their function as electron acceptors by themselves, but, also because of their function as a dryer of printing ink whereby they promote such reaction by the oxidation performed by such metallic constituents as an oxygen carrier. In other words, for the electrondonating surface of a pressure-sensitive copying paper, two kinds of compounds have been conventionally employed. One is a triphenyl methane phthalide compound such as crystal violet lactone which develops color as soon as it is adsorbed but later gradually loses this color by fading. The other is an acyl leuco methylene blue compound such as benzoyl leuco methylene blue which is gradually oxidized at the adsorbed state to develop color and maintains the color stability.

The compounds of cobalt, manganese, lead or the like used in the present invention strengthen the color development of the former and simultaneously promote the color development of the latter. In this regard, the present invention improves the life of copying paper the function of color development in a marked degree.

As for forms of the cobalt-, manganese, and leadcompound, a water insoluble inorganic salt which is produced by the reaction of aqueous solution in colloidal forms in the aqueous suspension containing paper grade pulp and clays of electron acceptor, is most preferable as a compound which performs the function of sensitizer physically and chemically.

The cobalt-, manganese-, and lead-compounds which are usable are: water-insoluble salts of inorganic or organic acids e.g. borate, phosphate, silicate, carbonate, sulfate, chromate, salts of resin acids, and salts of carboxylic acids or the like. Both bivalent and trivalent lead compounds or the like are useful. A mixture of different lead compounds is also useful.

The amounts of these metallic compounds to be incorporated into fillers of the present invention expressed by weight percent relative to weight of fillersare as follows:

Percent Lead 2-15 Manganese 0.5-4.5 Cobalt 0.3-2.0

A most remarkable effect can be attained when two or three kinds of metallic constituents such as cobalt-, manganese-, and lead compounds are used simultaneously as a mixture.

As for the kinds of clay, the above-mentioned electron accepting clays are useful.

The amounts of clays and cobalt, manganese-, or lead compound very according to paper making methods. They are dependent upon the retention of fillers. W'hen expressed by ash in finished paper, they are in the follow- When a cobalt-, manganese-, or lead compound is to be incorporated in paper, any of the following methods can be employed.

' (1) A method which synthesizes water-insoluble lead compound or the like in aqueous suspension containing pulp and clay, followed by paper making.

(2) A method which synthesizes water-insoluble lead compound or the like in aqueous suspension of pulp and then adds clay, followed by paper making.

(3) A method which synthesizes water-insoluble lead compound or the like in aqueous suspension of clay and then adds pulp, followed by paper making.

(4) A method which admixes pulp, clay and water insoluble lead compound or the like simultaneously, followed by paper making.

A more comprehensive understanding of the invention can be obtained by referring to the following illustrative examples which are not intended, however, to be unduly limitative of various conditions such as kind, form, amount, etc. of the fillers.

It is to be understood that any modifications derived from the following examples belong to the spirit and scope of this invention so long as they do not depart from the scope of the claims.

EXAMPLE 1 To 2% aqueous suspension of paper grade pulp, 10% aqueous suspension of attapulgite and 5% aqueous solution of cobaltous chloride were admixed uniformly and then while stirring, an aqueous solution of 41 B sodium silicate (approximately Na O-3-2 SiO diluted times as much water was added thereby to produce colloidal cobaltous silicate. The amounts of the above-mentioned raw materials were adjusted to afford the following proportions by Weight:

Paper grade pulp 100 Attapulgite 50 Cobaltous chloride 3 41 B sodium silicate solution 10 The pH of resulting aqueous mixed suspension was 8.9 and the weight and the ash content of filled paper made by the laboratory cylinder machine were 50 g./m. and 20.5% respectively.

EXAMPLE 2 Paper grade pulp 100 Terra alba 50 Manganous chloride 5 Sodium pyrophosphate 6 Locust bean gum 1 The pH of the resulting mixed aqueous suspension was 8.4. Filled paper made by the laboratory cylinder machine had a weight of 50 g./m. and an ash content of 25.0%.

EXAMPLE 3 To 2% aqueous suspension of paper grade pulp, 10% aqueous suspension of finely divided silicic acid produced by treating terra alba with sulfuric acid and 5% equeous solution of lead acetate were admixed uniformly. While stirring, 5% aqueous solution of borax was added thereby to produce colloidal lead borate. Further 10% colloid of melamine resin which had been made acidic by hydrochloric acid was added to improve the retention of fillers. The amounts of the above-mentioned raw materials were adjusted to afford following proportions by weight:

Paper grade pulp Finely divided silica 50 Lead acetate 10 Borax 9 Melamine resin 2 The pH of resulting aqueous mixed dispersion was 6.7. Filled paper made by the laboratory cylinder machine had a weight of 50 g./m. and ash content of 26.4%.

What is claimed is:

1. An internally filled paper for use in forming pressure-sensitive copying paper, said internally filled paper comprising cellulosic fibers, a clay, and a member selected from the group consisting of water insoluble salts of cobalt, manganese, lead and mixtures thereof, the clay and insoluble salt being present in an amount of 10-40% by weight of the filled paper, the salt being from 0.3 to 15% by weight of the total of the clay and salt, said clay being an electron acceptor clay capable of developing color by absorbing colorless electron donor selected from triphenylmethane phthalide compounds and acyl leuco methylene blue compounds.

2. An internally filled paper for use in forming presuresensitive copying paper, said internally filled paper comprising cellulosic fibers, a clay, and a water insoluble lead salt, the clay and salt being present in an amount of 1040% by weight of the filled paper and the lead salt being from 2 to 15% by weight based on the weight of clay and salt, said clay being an electron acceptor clay capable of developing color by adsorbing colorless electron donor selected from triphenylmethane phthalide compounds and acyl leuco methylene blue compounds.

3. An internally filled copying paper according to claim 2, in which the clay is finely divided silicic acid and the lead compound is lead borate.

4. An internally filled paper for use in forming pressure-sensitive copying paper, said internally filled paper comprising cellulosic fibers, a clay, and a water insoluble manganese salt, the clay and salt being present in an amount of 10-40% by weight of the filled paper and the manganese salt being from 0.5 to 4.5% by weight based on the Weight of clay and salt, said clay being an electron acceptor clay capable of developing color by adsorbing colorless electron donor selected from triphenylmethane phthalide compounds and acyl leuco methylene blue compounds.

5. An internally filled copying paper according to claim 4, in which the clay is terra al-ba and the manganese compound is manganese pyrophosphate.

6. An internally filled copying paper for use in forming pressure-sensitive copying paper, said internally filled paper comprising cellulosic fibers, a clay and a water insoluble cobalt salt, the clay and salt being contained in an amount of 10-40% by weight of the filled paper and the cobalt salt being from 0.3 to 2.0% by weight based on the weight of filler, said clay being an electron acceptor clay capable of developing color by adsorbing colorless electron donor selected from triphenylrnethane phthalide compounds and acyl leuco methylene blue compounds.

7. An internally filled copying paper according to claim 6, in which the clay is attapulgite and the cobalt compound is cobaltous silicate.

8. A method for preparing an internally filled paper suitable for forming pressure-sensitive copying paper, said method comprising adding to an aqueous suspension of cellulosic fiber, clay of electron acceptor capable of developing color by adsorbing colorless electron donor, a water insoluble salt selected from the group consisting of salts of cobalt, manganese, lead and mixtures thereof, and thereafter forming from the fiber suspension a paper, said clay and water insoluble salt being added to the suspension in respective amounts such that the quantity of clay and water insoluble salt is between 10 and 40% by weight of the filled paper and the water insoluble salt is from 0.3 to 15% by weight of the clay.

9. A method for preparing an internally filled paper suitable for forming pressure-sensitive copying paper, said method comprising adding to an aqueous suspension of cellulosic fiber, clay of electron acceptor capable of developing color by adsorbing colorless electron donor, a substance selected from the group consisting of water soluble salts of cobalt, manganese, lead and mixtures thereof, and a compound which reacts with said salt substance to convert the same in sit-u to water insoluble salt, and thereafter forming from the fiber suspension a paper, said clay, Water soluble salt and compound being added to the suspension in respective amounts such that the quantity of clay and water insoluble salt is between 10 and 40% by weight of the filled paper and the water 5 insoluble salt is from 0.3 to 15% by weight of the clay.

10. A method as claimed in claim 9 wherein the water soluble salt is cobaltous chloride and the insoluble saltproducing compound is sodium silicate whereby water insoluble cobaltous silicate is formed, the latter being present in an amount between 0.3 and 2% by weight of the clay.

11. A method as claimed in claim 9 wherein the water soluble salt is manganous chloride and the insoluble saltproducing compound is sodium pyrophosphate whereby insoluble manganous pyrophosphate is formed, the latter being present in an amount between 0.5 to 4.5%.

12. A method as claimed in claim 9 wherein the water soluble salt is lead acetate and the insoluble salt-producing compound is borax whereby water insoluble lead borate is formed, the latter being present in an amount between 2 to 15%.

References Cited UNITED STATES PATENTS 2,654,673 1 0/1953 Steinhardt 1l63 6.2 X 2,663,653 12/1953 Zimmerman ll7--3 6.2 2,902,399 9/1959 Paquin ll7-36.2 X 3,049,468 8/1962 Hinton et a1 l62181 S. LEON BASHORE, Primary Examiner. 

1. AN INTERNALLY FILLED PAPER FOR USE IN FORMING PRESSURE-SENSITIVE COPYING PAPER, SAID INTERNALLY FILLED PAPER COMPRISING CELLULOSIC FIBERS, A CLAY, AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF WATER INSOLUBLE SALTS OF COBALT, MANGANESE, LEAD AND MIXTURES THEREOF, THE CLAY AND INSOLUBLE SALT BEING PRESENT IN AN AMOUNT OF 10-40% BY WEIGHT OF THE FILLED PAPER, THE SALT BEING FROM 0.3 TO 15% BY WEIGHT OF THE TOTAL OF THE CLAY AND SALT, SAID CLAY BEING AN ELECTRON ACCEPTOR CLAY CAPABLE OF DEVELOPING COLOR BY ABSORBING COLORLESS ELECTRON DONOR SELECTED FROM TRIPHENYLMETHANE PHTHALIDE COMPOUNDS AND ACYL LEUCO METHYLENE BLUE COMPOUNDS. 